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Old 14-10-2012, 17:14   #301
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Re: Simple Solar For A Simpleton

The davit panel is 320W with a Vmpp of 54.7. It comes with #12 wire which we will hook up to #10 from the davits to the MPPT controller and then #4 from the controller to the battery bank.

The 2 doghouse panels are 140w each with Vmpp of 18. We're linking them in parallel with #10 wire via fuses and switches to a 'terminal bolt', and from there #6 wire to the batteries. I'll probably put a fuse in the line near the batteries too.

Then we head for Bermuda before the brass monkeys here are singing soprano, and down to the Caribbean to see if the panels help cut genny running time still further..... and to see the Caribbean

We've got genny time down to 2.5 hours per day which is half of where we were at the start of this thread

Vic
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Old 22-10-2012, 20:29   #302
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Re: Simple Solar For A Simpleton

One more trivial question.

With the above setup, the #6 wires from the 140 watt doghouse panels are going straight to the battery bank (after switches and fuses).
It works out that these wires would go right past the MPPT controller the the 320 watt davit panel feeds into.

The #4 wire from the controller goes to the battery bank.

Is there any reason why I shouldn't connect the #6 wires to the out #4 wires going from the controller to the battery bank.
It means just one pair of #4 wires going to the battery bank instead of #4 and #6 going seperately.
It just seems like a tidier arrangement.
I guess I'm asking if the #4 wires could cope.

Vic
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Old 22-10-2012, 20:37   #303
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Re: Simple Solar For A Simpleton

Quote:
Originally Posted by VirtualVagabond View Post
One more trivial question.

With the above setup, the #6 wires from the 140 watt doghouse panels are going straight to the battery bank (after switches and fuses).
It works out that these wires would go right past the MPPT controller the the 320 watt davit panel feeds into.

The #4 wire from the controller goes to the battery bank.

Is there any reason why I shouldn't connect the #6 wires to the out #4 wires going from the controller to the battery bank.
It means just one pair of #4 wires going to the battery bank instead of #4 and #6 going seperately.
It just seems like a tidier arrangement.
I guess I'm asking if the #4 wires could cope.

nearly 2/3 bigger with a short run,should be no problem

AWG to mm2

Vic
nearly 2/3 bigger with a short run,should be no problem

AWG to mm2
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Old 22-10-2012, 21:04   #304
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Re: Simple Solar For A Simpleton

Vic,

I make your total current about 35A absolute maximum (320W + 140W @ 13V). 4AWG will get you 20 feet (one way) from the output of the MPPT with 3% drop. I don't know your distance, but you won't generally be running at max output, so I would feel very comfortable with the #4 carrying the whole load to batteries unless the distance is much greater than that. The wire will easily handle the current, so it's only needed to limit voltage drop. Given the real currents you will actually be seeing I don't think you'll even see 3% most of the time, probably closer to 1.5%.
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Old 22-10-2012, 21:11   #305
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Re: Simple Solar For A Simpleton

Should be good but don't neglect to put fuses into the #6 wires near the join to the #4 wires. Or you could fuse the #4 at the batteries to protect the #6 wires (this will of course also protect your #4 wires). Check to see if you do that whether you will get nuisance blown fuses or not.
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Old 22-10-2012, 21:11   #306
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Re: Simple Solar For A Simpleton

It seems to confirm what I was thinking, but I just wanted to make sure I hadn't missed anything.
The distance from the controller to the battery bank is 9 ft one way so looks like it will work out just fine.

Thanks again

Vic
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Old 23-10-2012, 08:00   #307
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Re: Simple Solar For A Simpleton

Vic,

apologies, I left out one of your 140W panels above (thought about it in the shower this morning - strange). Doesn't change my overall conclusion, I still think #4 is fine, especially since your run is only 9 feet, but you may actually see 30+A somewhat regularly, as the maximum theoretical should be in the mid 40's. If you ever reached the maximum (which would require a cold sunny day, and it sounds like you would prefer the warm sunny variety) you could see a 2% drop in the #4 with your actual run, which is still in the acceptable realm.

Somewhat as an aside, that 2% drop really won't affect the house panels much, if any. Since you are running them directly connected they have voltage to spare. Even on a hot day the 140s will have a Vmp above 15V, so you can easily afford some voltage drop from those panels without affecting the amount they can put into your batteries. In theory a 2% drop might cost you something like half an Amp, mostly from the Sunpower panel, but only at absolute maximum production.
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